Please describe the errors you’re encountering and the community would be able to help you 😉
Answer these questions:
What WP Version?
What BB Version?
Did you do anything before the errors started?
Have you tried ”going” back and forth in your code/theme to see if changes might be the issue?

What are the errors? In case the users don’t have the right permissions to post, check your Forums Settings page and check the ” Allow all users of your multisite installation to create topics and replies” check-button 😉 If not, please describe your errors in detail/screenshots?

Cheers, Aron

Edit: I see your site now haha sorry – looks like the language files are missing?